In order to facilitate wireless communication at increasing data rates, various new standards and systems for mobile communication are emerging. Specifications for fourth generation (4G) mobile communication systems are being drawn up under IMT (International Mobile Telecommunication) Advanced. Future communication systems to be compliant with IMT Advanced require relatively wide RF (Radio Frequency) frequency bands, e.g. to accommodate relatively high bit rates. A problem that has been identified for communication systems compliant with IMT Advanced is that there is normally a lack of sufficiently wide free RF frequency bands; most frequency bands are fragmented, e.g. with different parts of a band being licensed for usage by different operators etc. Continuous frequency bands of e.g. 100 MHz bandwidth or more are normally not available. One way to address this problem is to set up a transmission link between a base station and mobile terminal using several sub bands that are scattered across a total frequency bandwidth to form an aggregated spectrum. An apparatus for receiving and processing RF signals such that multiple simultaneous access to different signal frequencies within an overall signal is provided, either within a common service band or spread over different service bands that are separated in frequency, is e.g. disclosed in U.S. Pat. No. 5,287,837.
The total frequency bandwidth of said aggregated spectrum may be considerably larger than the sum of the bandwidths of the sub bands combined. Normally, it will not be possible to determine the location of the sub bands in advance, e.g. due to that the location of available frequency bands may vary in time and/or with geographical location.
In order to facilitate reception of such aggregated spectrum signals, relatively hard requirements, e.g. in terms of bandwidth and/or dynamic range, may be set on radio-receiver circuitry components. This, in turn, results in relatively high power consumption in the radio-receiver components. However, in a mobile radio terminal, such as a mobile telephone, it is desirable to have relatively low power consumption, since the energy resources are normally limited by the capacity of a battery. In order to e.g. avoid excessively rapid draining of batteries in mobile radio terminals, there is a need for reducing the power consumption in radio-receiver circuits.